Significant Accounting Policies - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenues
Revenue	$ 365,451	$ 404,357
United States
Disaggregation of Revenues
Revenue	304,665	330,685
EMEA
Disaggregation of Revenues
Revenue	53,906	66,678
Other
Disaggregation of Revenues
Revenue	6,880	6,994
ITPS
Disaggregation of Revenues
Revenue	284,112	325,172
ITPS | United States
Disaggregation of Revenues
Revenue	223,326	251,500
ITPS | EMEA
Disaggregation of Revenues
Revenue	53,906	66,678
ITPS | Other
Disaggregation of Revenues
Revenue	6,880	6,994
HS
Disaggregation of Revenues
Revenue	64,049	61,343
HS | United States
Disaggregation of Revenues
Revenue	64,049	61,343
LLPS
Disaggregation of Revenues
Revenue	17,290	17,842
LLPS | United States
Disaggregation of Revenues
Revenue	$ 17,290	$ 17,842